Field
The present invention relates to microelectromechanical devices and especially to a microelectromechanical device, as defined in the preamble of the independent claim.
Description of the Related Art
Micro-Electro-Mechanical Systems, or MEMS can be defined as miniaturized mechanical and electro-mechanical systems where at least some elements have a mechanical functionality. MEMS devices can be applied to quickly and accurately detect very small changes in physical properties.
Motion limiters are commonly used in MEMS devices to control the maximum distance that a movable structure inside a device can displace. Another purpose for motion limiters is to dissipate energy in a controlled way in case a movable structure collides with an anchored structure inside a device due to a sudden high acceleration event. Such an event may occur, for example, when a device is accidentally dropped to the floor on a manufacturing line. Design limits are also at risk during element testing.
In collision, the primary purpose of a motion limiter is to protect the device from breakage by preventing fragile points of structures, e.g., sharp corners or narrow beams touching other surfaces. However, the motion limiter itself may also break if it is not robust enough. The robustness of a motion limiter can be enhanced, for example, by increasing the contact area between the contacting surfaces. However, this increases the risk of stiction between the contacting surfaces. Another conventional approach is to add flexibility to the impact such that the kinetic energy of the moving mass is transformed into potential energy within the motion limiter structure.
Efficient motion limiting is especially complicated in structures where a movable mass is designed to undergo out-of-plane linear or rotary motion above or between further structural layers. It is difficult to create truly robust structure without significantly increasing the size or complexity of the configuration.